Explorers have discovered ruins deep in a perilous South American mountain jungle that may unravel centuries-old archaeological mysteries – and reveal a fabulous hoard of Inca royal treasure.

In an adventure straight out of an Indiana Jones movie, a 260ft tall by 260ft wide structure 8,500ft above sea level in a dense cloud forest on the eastern flanks of the Andes in Ecuador has been unearthed by the multinational group.

Their initial theory suggests it could contain the Treasure of the Llanganatis, a huge quantity of gold and other riches supposedly hidden in the early 16th century by Inca general Ruminahui to keep it from the forces of Spanish conquistadors.

Legend says the general took the hoard up into the Llanganatis mountains and hid it in a cave or threw it into a lake.

He was captured and tortured by conquistadores but never revealed the location.

Explorers have already found various artefacts on the flat roof of the structure – perhaps the mausoleum of Atahualpa, the last emperor of the Inca people who was executed by the Spanish – where sacrifices may have taken place.

Archaeology: The discovery is like something out of an Indiana Jones film (Photo: Handout)

Located in Ecuador’s Llanganates National Park, the site is only 20 miles from the town of Banos de Agua Santa, a popular adventure tourism centre and a gateway for tours into the Amazon basin.

But it can currently only be reached by an 8-10hr trek through thick mountainous jungle (sorry, Dr Jones, there are some snakes!) and the structure is tricky to examine in detail as much of it is caked in undergrowth and thick moss.

The Ecuador government is now backing an official archaeological expedition to explore the site and one day hopes to be able to open it up to adventurous holidaymakers.

A tourism ministry spokesman said: “We would hope to be able to share this find with both local and foreign visitors, offering them a unique insight into our ancestors’ rich heritage and culture.